Magnetostrictive transducer



H. w. SCHAFFT 3,339,132

MAGNETOSTRICTIVE TRANSDUCER U l U Filed Dec. 30. 1964 Inventor HUGO W. SCHAF FT FIG 3 FIG. 4

Aug. 29, 1967 United States Patent 3,339,132 MAGNETOSTRICTIVE TRANSDUCER Hugo W. Schafit, Des Plaines, Ill., assignor to Motorola, Inc., Franklin Park, 11]., a corporation of Illinois Filed Dec. 30, 1964, Ser. No. 422,273 3 Claims. (Cl. 318-118) This invention relates to a magnetostrictive vibrator and more particularly to an ultrasonic magnetostrictive transducer having spaced laminations.

A typical use of an ultrasonic transducer is in a cleaning operation in which the device imparts ultransonic energy to cleaning fluid in a tank. The ultrasonic energy so generated is notably effective in degreasing and reaching certain areas of the object to be cleaned which are generally inaccessible to normal cleaning methods.

The operation of an ultrasonic transducer of the above type is known. If a voltage is impressed upon a coil of wires surrounding a magnetostrictive rod, the rod will vibrate at the frequency of the applied voltage with an amplitude roughly proportional to the voltage magnitude. This results in ultrasonic waves being radiated from the ends of the rod. Using a solid rod, however, is inelficient because of eddy currents which flow in the material and hysteresis. For this reason magnetostrictive oscillators are usually constructed of thin tubes or laminations, fastened together to form a single solid core.

Transducers made of material such as nickel convert only approximately 40% of the electrical energy into mechanical energy with the remaining 60% being converted into heat. To avoid overheating the transducer can be cooled either by being placed in a liquid by conduction or in still or moving air by radiation and convection. In order to provide maximum surface area for cooling by radiation and convection spaced lamination transducers are used. Present spaced lamination transducers, however, are constructed by hand assembling individual sheets, which require fastening or bonding together, to form an integral core, This process requires a substantial amount of time to complete, because it is necessary that the space between each lamination be as uniform as possible for maximum operating efliciency.

It is an object of this invention to provide an improved spaced lamination, ultrasonic magnetostrictive transducer.

It is another object of this invention to provide a spaced lamination ultrasonic magnetostrictive transducer that is simple to assemble, thereby reducing labor costs.

It is still another object of this invention to decrease the number of parts required to provide a suitable spaced lamination ultrasonic magnetostrictive transducer thereby reducing the material cost.

A feature of the invention is the provision, in a spaced lamination ultrasonic magnetostrictive transducer, of a single strip of magnetostrictive material which is repeatedly folded back upon itself in zig-zag fashion to form a plurality of spaced laminations, each lamination integral along the fold of the preceding lamination, and means for providing a time varying magnetic field about the laminations.

Another feature of the invention is the provision in a spaced lamination ultrasonic magnetostrictive transducer of a single strip of magnetostrictive material that has punched slots such that when the strip is folded back upon itself to form a plurality of spaced laminations, the slots are aligned in a channel through the transducer.

Still another feature of the invention is the provision in a spaced lamination ultrasonic magnetostrictive transducer of the vibratory faces of the transducer defined by the edges of the laminations transverse to the folds of the magnetostrictive strip being either rectangular or circular in configuration.

'allel to the unidirectional In the drawing:

FIG. 1 is a plan view of the magnetostrictive material of the invention prior to being folded into spaced laminations;

FIG. 2 is a perspective view of a completed transducer assembly of the invention;

FIG. 3 is a schematic diagram showing a circuit for energizing the assembly of FIG. 2; and

FIG. 4 is a plan view of a second embodiment of the transducer assembly.

In practicing the invention a single strip of magnetostrictive material is punched with slots and then repeatedly folded back upon itself in zig-zag fashion to form a core having a plurality of spaced laminations, each lamination integral along the fold of the preceding lamination. The core has a first vibratory face defined by the edges of the laminations transverse to the bend of the magnetostrictive strip and a second vibratory face defined by the opposite edges of the lamination. The punched slots are aligned to form a channel through the core when the magnetostrictive material is folded into laminations. Coil windings are then wrapped around the opposing sides of the channel and pass through it. Direct current means coupled to the coil bias the core into having a unidirectional magnetic field through the laminations. An alternating current means also coupled to the coil applies a signal of resonant frequency to energize the same thereby exciting the vibratory faces into movement at resonant frequency and in a direction parmagnetic field.

In FIG. 1 of the drawing can be seen a magnetostrictive strip 11, which can be made out of some typical magnetostrictive material such as nickel or Invar (a nickel-iron alloy) having punched slots 13. To make the core 15 of the spaced lamination transducer 16, the magnetostrictive strip 11 is repeatedly folded back upon itself generally along the dashed lines 17 in a zig-zag fashion to form a plurality of rectangular shaped spaced laminations 14. Each lamination 14 is integral along the bend or fold 19 of the preceding lamination. The core 15 has a first vibratory face 22 defined by the edges of the laminations 14 of core 15 transverse to the bend 19 of the magnetostrictive strip 11, and a second vibratory face 20 defined by the opposite edges of the laminations 14. The face 22 is fixed to the bottom 23 of the tank 33 in some manner such as by copper brazing or silver soldering. The frame 35 held by screws 40 supports the bottom of the tank 23 and support post 42.

When the strip 11 is folded into the spaced laminations 14, the punched slots 13 are aligned to form a channel 25 through core 15. Wire of sufiicient size to permit both AC and DC currents to flow without excessive heating is then passed through the channel 25, wound around the opposing sides 27 and 28 thereof, and connected in series to form coil 30. The magnetic field is closed by the ends 31 of the lamination 14 which eliminates flux leakage. Since this is the function of the ends 31, the cross-section of the end should always be greater than a cross-section of any leg. Therefore, the longitudinal length of the punched slot 25 must be chosen carefully to insure that the end 31 does not offer any greater resistance to the flux than the resistance in either leg.

FIG. 3 is a schematic diagram showing the basic operation of the transducer 16 mounted against a thin walled tank 33. This is only an example of one use of the transducer and is not meant to be construed to limit the us of the invention. A source of alternating current 34 is coupled through a transformer 36 to blocking capacitor 37. A direct current source 38 is coupled through choke coil 39 and combined with the alternating current from capacitor 37 to flow through coil 30. The capacitor 37 is tuned to the reactance of coil 30 so that the coil 30 appears as a receptive load to the alternating current source 34. Transducers are usually operated at resonance, which frequency is determined by the length of the magnetostrictive material, as this is the point at which they will undergo maximum vibration together with maximum stress and strain in the material. The mechanical power output is directly proportional to the dynamic strain level so the higher the strain in the core, the higher the mechanical energy produced. Using this principle, the strip 11 is folded into laminations 14 that are longer than they are wide. By doing this the resonant frequency in the longitudinal direction is different than that in the transverse direction. Therefore, when a frequency is applied to the transducer 16 which is equal to the resonant frequency of the longitudinal length of the material; for example 25 kc., there will be an excursion in this direction rather than in the transverse direction. By having the vibratory faces 22 and 2t) defined by the edges of the laminations 14 of core 15, transverse to the bends 19 of the magnetic strip 11, it is assured that maximum vibration will occur at these faces 29' and 22 which vibrate off the nodal point 44- at which point there is a minimum of motion and a maximum of stress. By having face 20 operate unloaded in the air the vibrational output of face 22 mounted against the tank bottom 23 is increased.

If the core were totally unmagnetized, every time a flux were set up by the alternating current source 34, it would shorten the core without regard to the flux direction. The transducer 16 would then vibrate at twice the frequency of the exciting AC voltage. The direct current, therefore, is used to magnetize the core 15. This results in the core 15 having a unidirectional magnetic field such that it will vibrate at the same frequency as the frequency of excitation. With the transducer 16 mounted against the thin wall of tank 33 the ultrasonic waves produced by the vibratory face 22 will be transmitted through the tank bottom 23 and into the liquid Within the tank FIG. 4 illustrates another embodiment of this invention where the vibratory faces and 22, rather than being square or rectangular in shape as shown in FIG. 2, have a round configuration. The principle of operation is identical as described for the transducer 16 of FIG. 2, and it is useful in those situations where a round transducer would be structurally desirable.

This invention provides, therefore, a spaced lamination transducer Where the core is constructed solely of one continuous strip of magnetostrictive material folded into spaced laminations. This construction eliminates the tedious task of assembling individual laminations into a core thereby reducing labor costs. In addition, as it is not necessary to insulate the individual laminations nor bind them together to form the core, savings are gained through reduced material requirements.

What is claimed is:

1. A magnetostrictive transducer including a singlecontinuous strip of magnetostrictive material having a plurality of spaced alternating folds forming a core of spaced laminations, each of said laminations having a slot therethrough, said slots forming a channel having opposing sides and extending through said core, each of said laminations being integral and forming a closed loop around said channel, said core having a first vibratory face defined by the edges of said laminations transverse to said colds of said magnetostrictive strip, and a second face defined by the opposite edges of said laminations, coil means passing through said channel and encircling said opposing sides of said channel, alternating current means coupled to apply a signal to said coil to energize the same thereby exciting said vibratory faces into movement.

2. A magnetostrictive transducer including a single continuous strip of magnetostrictive material having a plurality of parallel spaced alternating folds forming a core of parallel spaced laminations, each of said laminations having a slot therethrough, said slots being concentrically aligned with each other and forming a channel having opposing sides and extending through said core, each lamination integral along the fold of the preceding lamination and forming a closed loop around said channel, said core having a first vibratory face defined by the edges of said lamination transverse to said folds of said magnetostrictive strip, and a second face defined by the opposite edges of said laminations, said first and second faces having rectangular configurations, coil means passing through said channel and encircling said opposing sides of said channel, alternating current means coupled to said coil means for providing a time varying magnetic field about said spaced laminations for periodically shortening and lengthening said laminations in a direction parallel to said magnetic field.

3. A magnetostrictive transducer including a single continuous strip of magnetostrictive material having a plurality of radially spaced alternating folds forming a core of radially spaced laminations, each of said laminations having a slot therethrough, said slots being circumferentially aligned with each other and forming a channel having opposing sides and extending through said core, each lamination integral along the fold of the preceding lamination and forming a closed loop around said channel, said core having a first vibratory face defined by the edges of said lamination transverse to said folds of said magnetostrictive strip, and a second face defined by the opposite edges of said laminations, said first and second faces having circular configurations, coil means passing through said channel, alternating current means coupled to said coil means for providing a time varying magnetic field about said radially spaced laminations for periodi cally shortening and lengthening said laminations in a direction parallel to said magnetic field.

References Cited UNITED STATES PATENTS 2/1950 Nahman 29-155 2/1965 Hayes 318-118 

1. A MAGNETOSTRICTIVE TRANSDUCER INCLUDING A SINGLECONTINUOUS STRIP OF MAGNETOSTRICTIVE MATERIAL HAVING A PLURALITY OF SPACED ALTERNATING FOLDS FORMING A CORE OF SPACED LAMINATIONS, EACH OF SAID LAMINATIONS HAVING A SLOT THERETHROUGH, SAID SLOTS FORMING A CHANNEL HAVING OP POSING SIDES AND EXTENDING THROUGH SAID CORE, EACH OF SAID LAMINATIONS BEING INTEGRAL AND FORMING A CLOSED LOOP AROUND SAID CHANNEL, SAID CORE HAVING A FIRST VIBRATORY FACE DEFINED BY THE EDGES OF SAID LAMINATIONS TRANSVERSE TO SAID COLDS OF SAID MAGNETOSTRICTIVE STRIP, AND A SECOND FACE DEFINED BY THE OPPOSITE EDGES OF SAID LAMINATION, COIL MEANS PASSING THROUGH SAID CHANNEL, AND ENCIRCLING SAID OPPOSING SIDES OF SAID CHANNEL, ALTERNATING CURRENT MEANS COUPLED TO APPLY OF SIGNAL TO SAID COIL TO ENERGIZE THE SAME THEREBY EXCITING SAID VIBRATORY FACES INTO MOVEMENT. 